Dual propeller



June 6, 1944. 4, 1'. R. TARN 1 2,350,942

DUAL PROPELLER Filed Oct. 17, 1940 4 Sheets-Sheet 1 INVENTOR June 6,1944. T. R. TARN 2,350,942

DUAL PROPELLER F iled Oct. 17, 1940 4 Sheets-Sheet 2 s. H. P. POUN DS RATIO THRUST TO SHAFT HORSEPOWER (IN POUNDS) R.P. M.

ill I: :11: iii ll I: I

INVENTOR im 0?.

June 6, 1944. T, R, TAR-N DUAL PROPELLER Filed Co t. 17, 1940 54 Sheets-Sheet 5 PROPELLING FORWARD BACKING 20w54o mm uzo mom ooEwa wit.

DIRECTION OF REACTION AND WHEEL STREAM I 3 g. In ORW NEE i mwo RPT mom BACKING WHEEL DIRECTION OF THRUST AND MOVEMENT OF BOAT PROPELLING WHEEL FLDATS IN WAKE ADVANCE OF WHEEL THROUGH WATER INVENTOR June 6, 1944. 'r. R. "IA RN DUAL PROPELLER Filed Oct. 17, 1940 4 Sheets-Sheet 4 INVENTOR 35W a? 521W zwmf Patented June 6, 1944 UNITED STATES PATENT f OFFlCE DUAL PROPELLER. Thomas Tarn, Pittsburgh, Pa.

Application October 17, 1940, Serial No. 361,485

3 Claims.

This inventionrelates to new and improved fluid actuating propeller arrangements. And, more particularly, it pertains to the handling and steering of vessels such as tow-boats or craft that are provided with actuating propellers of the screw type.

The successful navigation of inland streams and rivers requires the incorporation of features in power craft builded for such purpose that will enable the operators to handle the craft in spite of restricted depth of the streams, tortuous channels, bends andturns, variations in the swiftness of flow, trafiic conditions, seasonal variations, and other contingencies that complicate the problem of building power craft for safe and expeditious movement of tows or of a fleet 'of tows or barges. That is, it is customary for a towboat to propel a group of tows or barges from port to port. For many years the so-called paddle Wheel or stern wheel type of river boat has been used on the western rivers of this country. Later, the so-called screw type of propeller ,boat was introduced from foreign sources, being designed primarily asa packetv or free running boat and not for towing barges on; the head in the time-proven and economical manner employed on the Ohio and Mississippi River system. v

In its original conception, the imported craft was an utter failure as compared with the sternwheel boat in its ability to maneuver large tows of heavily laden barges. I was able to make certain constructional changes in the hull design and arrangement of the underwater appurtenances in a screw-type of river boat or craft. that would effectively increase its propelling and handling ability, particularly from the standpoint of the operation of the rudders. As shown in my Patent 1,327,643, a twin-screw tunnel type of boat provided with propellers .ad jacent opposite sides thereof and with suitable governing rudders, could be greatly increased in appreciated from a study of the chart of Figure 65 4 of the drawings wherein the full line curve A shows the thrust per shaft horse power of a screw propeller for a scaled speed'range where a conventional single propeller is propelling ahead. The dotted curve C shows the relationship where the'same propeller wasreversed to move the boat astern. The drop-off in horse power and thrust is substantial'and'is particularly great from a percentage standpoint-due to uncontrollable structural factors. It is thus apparent that for the present state of the art, the loss of effective thrust entails'a material loss of efficiency. This is an important loss where a boat is to be used for the above-mentioned purposes and must be maneuvered within limited space requirements as when entering or leaving a lock chamber or navigating between bridge piers or other structures of an engineering character.

flanking rudders of the same large area as the steering rudders. And, the'position of the flanking rudder in the propeller wake of least velocity where the propeller is rotated for a backing flanking operation constitutes another important factor from the standpoint of maneuvering the tow. 'An increased efiectiveness in backing would automatically increase the effectiveness of flanking, and if this is obtained, the twin-screw type of tunnel boat will be established as the equal or superior'in all"respects to the sternwheel type'of boat as an outstanding power medium to meet the demands for safe andexpeditious movement and control of large tonnage when assembled or grouped in the accepted western river fashion.

Ordinarily boats move forwardly a greater part of the time; consequently in designing propellers it is usual to provide propelling surfaces that favor forward propulsion. Those; skilled in the art known that blades of the propellers should have certain shape characteristics for maximum efficiency and effectiveness of propul sion. When these characteristics are incorporated in the ahead propulsion surfaces the needed metal structure for providing strength to the blades constitutes a factor precluding and not conducive to the best shape characteristics of the backing faces of the blades for an opposite direction of propulsion, i. e., astern. To provide strength and rigidity of the blades, it has been customary to shape the backing face portion of a blade in a convex or bulging manner. This so-called backing face is efiiciently inactive as far as propulsion is concerned. For example, as pointed out above, the effective horse power for backward or astern movement will be materially less than the horse power available for forward movement, due to the lost efliciency of the propeller screw action when the screw is reversed and the backing face portions are employed to produce thrust. Many attempts have been made by those skilled in the art to form'the shape of the backing or reinforcing face to increase the efficiency of the backward movement of the boat, but have met with little success.

In view of the above considerations, it has been an obje t of my present in ention t e e op a p ope ler ar aneementha in heabi y of ovins. a boat ahead or as ernwit equal cil ty and great e cien y than poss heretofore.

Anotherobieet h s be n ode e oat ra sement t t w ll furth r imp tsm ip verab itv ;and;ove -a ieieney or operation on eraetu lr orlrins con t ons;

a'fu ther'o i j t has b t p ide anarr ns ment f i reasing h maneuverability of a boa p rtic larl irom th a p i t f t fl nkin op r t on.-

These and many other j s o my inventi n il a pear to hose skil ed i t e a t from t e drawin s, h la ms-and th spe f ti n.

n th drawin s F u :1 is a som what diag ammatic f a ntal elevati s owing a pr pulsi n arrangement embodying my invention and incorporated a tw -sc ew c am or tu n l type f boat;

Fi ure 2 s a somewh t dia ramm ti r u o the p opeller a ran m emp ed nt e boa o Fi ure shaft with blades of substantially identical dimensions and of the same hand, with their most efficient propelling surfaces locked face to face inwardly on the shaft, and in a suitable angular relation.

It was'found as the result of a tank test that the facing of the most efficient propelling surfaces outwardly did not provide the most effective thrust results, although they were better than heretofore possible with a single propeller arrangement. Thus, in general, corresponding blade surfaces of the two propellers of my invention face in opposite directions; and preferably, the eificient surfaces oppose or face each other. The left-hand portion shows the wheel stream, th direction of movement of the boat, etc., where the shaft is reversed to effect an astern movement of the boat; the right-hand portion shows the relationship when the shaft is moving in its ordinary propelling direction to advance the boat ahead. In this figure, the blades are shown for a complete revolution of the shaft, namely, for an operation between 0 and 360,,- both as to astern .or backing and as to ahead or propelling operations.

Figure 8 is a partial sectional view in vertical elevation along the linesof Figure 1 showing an adaptation of apparatus of my invention to an existing or conventional boat and shaft arrange- F u es is. a omparative est cha t of a sin le pr peller arran em nt as co tr e an op rated prior o my inventio a d. o a p op l r as oopstruet dar d o e ted i cc da c th 5 my invention; In th ha t, .1. ep s ts propeller shaft orse power. In the curve A,'t, rela between thrus pe haf h r pow r to spe d... the shaft is plo ted fo the con n l sin le prope ler as opera d t dv e a boat ahead andthe brok n- .line C s thesam propelleroperated to move the boat astern. Broken Figure 7 is a diagrammatic chart representing the fluid actuation 'bythe blades of each propeller wheel of a dual propeller arrangement constructedin accordance with my invention. In laying out this diagram, I contemplate the use of a pair of propeller wheels such as shown in Figures'l, 3,- and {7 havinga spaced-apart relationship on. a common actuating tail or. propeller ment, requiring the provision of a new fairwater;

Figure 9 is a similar View showing a modified adapting arrangement wherein the tail .or end of the propeller shaft is provided with a longer taper turn thereon for receiving the longer sleeve coupling of my propeller combination; in this arrangement, an extended sleeve coupling is provided to compensate for the extension of the taper into the propeller hub. This is alsotrue of the arrangement of Figure 10.

Figure 10 shows another adaptation wherein the tail shaft is pushed or extended backwardly and the propeller hub shaped so that its fore portion corresponds to the adjacent cylindrically shaped portions of the tail or propeller shaft;

Figure 11 is a side sectional detail similar to Figure 3, but showing a modified dual propeller arrangement; and

Figures 12 and 13 are transverse sectional views taken on line XII.X[I of Figure 11 and illustratinghow an angular relationship of the propellers may be changed about the shaft or axis of rotation.

While in previously mentioned views I show a solid or integral hub for the, propeller pair, I contemplate, as shown in Figure 11, the attachment of propellerblades to separate hubs; among other thin s, such an arrangement obviates the necessity for renewing the entire arrangement in the eventv that one of the blades is damaged.

Although the present invention was developed particularly from the standpoint of river and other boats requiring considerable maneuverability, it is apparent that its application is not limited to this type of boat or craft and that it can be applied tomotor boats, sea-going vessels, etc., and to the excitation of fluids generally.

Inaccordance with the present invention as shown, for example, in Figure 1, I provide a pair of propeller blades 30 and 3| that in the present embodiment of my invention are cast on a common hub portion 32. Assuming that a counterclockwise rotation of the propeller screw will be employed for forward propulsion and that a clockwise rotation will.be employed for propulsion astem, then the blade relationship of Figure 1 will apply; the clockwise-counter-clockwise rotationrelation maybe reversed by changing the angular'ity of the blades. In this relationship, the fore propeller 30 has its relatively efficient propelling surface facing aft and opposite to the direction of movement of the boat. It-is thus apparent that the wheel-30 will be active in the forward propulsion of the boat, see the blades indicated l-d; inclusive, of the fore wheel propeller 30 during the advance of the boat, as shown to the right of- Figure 7.

On. the. other hand, the aft propeller Wheel 3| has thefc'onivex or curved backing surface portion of its blades facing aft and its more efficient surfaces facing forwardly of the boat. Thus, the backing -or curved surface portions face in the direction of forward movement of the boat and the efficient operating surface portions face in the direction of backward movement of the boat and are effective for backing action when the propeller is being moved clockwise in the specific example chosen for the purpose of this discussion, see the blades represented diagrammatically V4 in the left portion of Figure 7 of the drawings. As will be noted, the active propulsion surfaces of the fore propeller 30 are adjacent to the active propulsion surface of the aft propeller 3 l see Figure l.

Aigene'ral arrangement such as above set forth shows'one propeller 30 with its effective operating faces and its backing faces located for forward propulsion of the boat and a second propeller' 3| spaced-apart from the first propeller and preferably in axial alignment on the same shaft withits propulsion and'backing faces facingin' an adjacent and "relatively parallel alignment to those of'the first-mentioned propeller, or in such a manner that the blades of the second mentioned or aft propeller 3| will have their faces arranged for highly elficient backing movement.

The question arises as to whether a pair of propellers of the same hand having adjacentlyfacing propulsion surfaces can be eifectively employed with any degree of efficiency in a screw propeller type of boat when they are installed on streams of the blades of the active propeller wheel will pass through the spacing between adjacent propeller wheels and between the spacing of the blades of the floating propeller with a minimum obstruction to flow. This is' due to the relative relationship and angularity of the blades of the propeller wheels; taking into consideration the slip stream and blade velocities.

From the above discussion, it'will be apparent that the relative distance or cooperatively advanced relation between propeller wheels may be regulated axially to conform to the speed of rotation and the pitch angle or angles of the blades to provide additional compensation in time and distance, in order that the propeller wake or slip stream issuing from the blades of the active propeller will pass substantially directly by or between the blades of the floating or inactive propeller with a minimum of distortion and interference. The entire arrangement due to its simplicity also eliminates the a common shaft that is actuated by a common prime mover; By actual tests, it has been definitely determined that. sound naval and r engineering principles are not violated in employing a pair of propellers of the same hand so mounted for commonrotation ahead or astern on the sarn ea'xis. Such tests show that when the dual propellers are'suitably arranged, one can be effectively employed for one direction of movement of the boat without setting up prohibitive operating reactions with the other propeller.' In the present arrangement, during the forward propulsion, the backing propeller 3|, in effect, floats in the wake or slip stream, and vice versa, during the backing operation when the backing propeller is the active one. The distance between propellers is selected upon considerations of the contemplated speed of operation of the propeller shaft as well as from the standpoint. of the pitch, area, and number of the blades. 7 The radial angular location of the blades of one propeller with respect to that of the other propeller in a preferred arrangement is sub: stantially the same, and depending upon the desired speed. of operation and the distance between the propellers on the shaft, the wheel or slip 75 need for additional appendages or protuberanc'es that normally produce turbulence and eddies.

Such an installation ofan additional propeller on the same extension of the tail shaft which takes the usual propeller has been found-to involve no interference with or restriction of the space such as would prevent the maintenance offree andunobstructed flow of the water. That is, the propeller arrangement of my invention can be readily applied to existing boat installations as illustrated, for example, in Figures 810, inclusive. I

Since as indicated onthe curves of Figure 4,

my arrangement of propellers makes possible the same propulsive effect in ahead and'astem movementsof the boat and very materially in-- creases the backward efiiciency over the normal efficiency of the conventional propeller, it will be apparent that it makes possible a surprising increase in checking, backing, and maneuverability of a boat employing the features thereof. It navigates in extremely high or swift current to much better advantage than any river boat of the conventional propeller type. It is believed that the present invention is the fulfillment of the last need or requirement in the operation of screw propeller type of boat to place such operation on entire parity, with a stern-wheel type of boat in all departments, and particularly, from the standpoint of its ability to back with full power as against a fraction of the amount under present installations. The arrangement overcomes the effldefects ofattempting to employ the back- ;es of a propeller'for propulsion astern. As intimatedabovea convex backing surface is formed primarily from the standpoint of strengtheningand reinforcing the efiicient propelling face or surface of the blade. The present arrangement also to a marked extent increases the ability of the boat to respond to rudder re actions, due to the impingement or reaction of a wake stream having'higher velocity. Againreferring, to Fi ures 1, 2, and'3, I have therein" shown a propeller apparatus embodying my inventionas applied to a chambered or tunneltypeof twin screw tugboat l0 having a drive shaft combination:'20 consisting of a primary shaft '22 and a protective tubingZI. The shaft 22 extends through stern bearings 23 of theboatlil and is journaled within bearings 25 supported'by a vertical post or V struts 24 and having a rope guard 26. Aconventional rudder arrangement has been shown, and full details relating to the. same may be obtained from a studyof my'Patent 1,327,643. A steering rudder l2 may beof the partially unbalanced type; 14 designates a-flanking propeller that may be of the balanced or unbalanced type. Further details as to the rudder arrangement are omitted in that thepresent invention does not pertain thereto. In the'sectional detail of Figure 3, it will be noted that the-two propeller wheels 30 and 3| comprise blades cast on a common hub 32 that is suitablykeyed on a tapered end portion 21 of the propeller or tailshaft 22. A fairwater or protective cap 35 is removably secured by cap screws 35 upon end portions of the hub 32. A nut 34 removably locks hub 32 upon the tapered tail shaft end 27. I

.In the embodiment of my invention shown in Figures 5 and 6, I have illustrated a single engine, single screw boat having a propeller shaft provided; with wheels -31 that are mounted in the manner shown inFigure 3. In this arrangement, a single rudder 42 is operably positioned inthe usual manner between the counter and rearwardly extending portion 43 of stem frame 44 ofthe boat 40.- 1 H In Figure 8, Lhave shown an apparatus arrangement for, adapting my invention to an existing propeller ortail shaft without changing its positionor extension. The two propellers 30and 3| are formed as a single casting on hub 32, the forward portion of the hub corresponding to the ordinary hub of an ordinary propeller to fit over the usual tapered end portion 21a of the propeller shaft, and the adjacent aft portion is recessedto receive a specially formed fairwater 45 havinga cylindrical portion 41 that is adapted asa nut to engage a threaded portion 28a of the tail shaft 22a. g t In Figure 9,.1 have shown another arrange- .n which the propeller shaft combination 22a is provided with a coupling sleeve l9b that is additional to conventional sleeves I9 in such a manner that the shaft can be separated enough to compensate for the extension thereof necessary for the propeller wheel 3!. The end of the shaft 21b is tapered along alength portion corresponding to the length of the hub of the propeller unit. A usual form of fairwater cap arrangement 34 and 35 may be employed. Figure 10 is an arrangement similar to Figure9 in that the shaft is extended in the same manner but no. attempt is made to provide a full tapered engagement with the length of the propeller'hubs In other words, the ordinary form of hub arrangement is employed inwhich the fore portion 214; is tapered vention-is that the increased velocity, of slip stream, made possible by thehigher backing efficiency, materially increases the'reactive efiecity; the fore arrangement being clutched out for ahead movement; the aft arrangement being clutched out for astern movement. By employ,- ingthe dual propeller arrangement of myinvention-fore and aft of such a boat, I eliminate the need for clutching or cutting out one arrangement and .decrease the'propeller horse power requirements by substantially one-halfmaneuverability will have a marked increase. Of course; a single dual-propeller arrangement fore or aft ofthe boat can also be utilized, since as previously pointed out,-the.thrust or efiiciencyis the same for ahead andastern' boatmovement. Other uses and applications of my invention'will appear to those skilled in the art of fluid actuation.

Although I have for the purpose of illustration shown my invention as applied to a twin-screw type of propeller boat in Figures 1 and 2, and as applied to av single-screw type of tug in Figures 7 and 8, it will be apparent that it can be readily adapted to other arrangements and that its principles are, in general, applicable to any. conventional craft arrangement whether for use on river, lake, or ocean. For example, my twin propeller arrangement can be effectively utilized with a high efiiciency in a sleeve or shroud wherein, the propellers operate within a substantially enveloping cylindrical arrangement.

Although in an ordinary installation I prefer to select the spacing between the pair of propellers aswell as the radial angular relationship of the blades of one propeller with respect to the blades of the other propeller upon the basis of a contemplated. operation of the craft or boat in question, and to then cast them in this relation,

I also contemplate providing means for adjusting the radial angular relationship of the blades tiveness of the vfluid stream upon the flanking 7v rudder or rudders. This: is true since rudder 'action is directly dependent upon the velocity of water projected upon a rudder surface.

and the distance between blades after the propeller wheels have been formed. As shown in Figures Hand 12,- I provide the propeller wheel 3 with a hub 52 that is separate from a hub 53 of the wheel 3|. Space rings or shims 54 are provided between the hubs 53 and 54 to permit adjustment of the spacing between the propeller wheels on their common actuating shaft 22. The radial angular relation of the blades of wheels can be adjusted by removing the longitudinal mounting single key 55 from keyway-SE and turning one of the wheels withrespect to the other; the single key 55 can then be replaced bytwo keys one of which can be distorted as indicated by 55 in Figure 13 to hold the wheels-in their adjusted relationship. Figures 12 and 13 show one blade 39, as angularly shifted fromposition aa to position bb; either or both of the propeller wheels may be thus radially-angularly adjusted.

I contemplate tilting or providing an angular rake of the blades or an expanded pitch toward their tips as circumstances may require and as practised in the present state of the art as to conventional single propeller arrangements. It is apparent that each wheel may be provided with a suitable number of blades, although I prefer to provide blade. pairs having substantially the same characteristics and dimensions... Pro

peller arrangements of my invention can also be employed at any suitable location with respect to a craft or boat such as at'fore,-aft, port, or starboard positions, or any combination of these positions; v I In' view of the above considerations, it is ap parent that many modifications, additions, subtractions', adaptations, and changes can be made without departing from the spirit and scope of my invention as indicated in the appended claims.

I claim:

1. A propulsion system for a screw propeller type of craft comprising a pair of propeller blades, each of said blades having the same hand, one of said blades being axially spaced from the other propeller blade, each of said blades having a face of substantially planar outline and a backing face of substantially curvilinear outline, the planar face of one of said blades being positioned in an opposed and facing relationship with respect to the planar face of the other blade in such a manner that one planar face will effect forward movement of the craft and the other planar face will effect aft movement thereof.

2. A propulsion system for a screw propeller type of craft comprising a hub portion, a set of propeller blades extending radially in substantially peripheral alignment from a portion of said hub, a second set of propeller blades extending radially outwardly from a portion of said hub in substantially peripheral alignment behind and in axially spaced relationship with respect to the first-mentioned portion thereof, the blades of each set having one substantially planar face portion and a substantially curvilinear face portion, the planar face portions of the blades of one of said set being operably positioned in an opposed and facing relationship with respect to the planar face portions of the blades of the other set.

3. A propulsion system for a screw propeller type of craft comprising a hub portion, a set of propeller blades extending radially in substantially peripheral alignment from a portion of said hub, a second set of propeller blades extending radially outwardly from a portion of said hub in substantially peripheral alignment behind and in axially spaced relationship with respect to the first-mentioned portion thereof, the blades of each set having one substantially planar face portion and a substantially curvilinear face portion, the planar face portions of the blades of one of said set being operably positioned in an opposed relationship with respect to the planar face portions of the blades of the other series, the blades of one series being positioned in substantial alignment with respect to the blades of the other series with respect to a longitudinal axis of said hub.

THOMAS R. TARN. 

